High voltage power supplies suitable for use in electrophotographic copying machines are known in the art. For example, one such power supply is disclosed in U.S. Pat. No. 3,986,085 for Corona Power Supply Circuit, issued to Harold J. Weber on Oct. 12, 1976. In the cited example, an oscillating circuit produces a series of pulses which are shaped and applied through a step-up transformer to a voltage multiplying circuit. The multiplying circuit provides the desired output voltage.
In certain electrophotographic applications, it is further desirable that the power supply output voltage be regulated in such a way to permit desired rapid changes in the output voltage, for example, where it is desired to quickly change the bias voltage on the developer in order to pin white vectors and provide for toner concentration control as well as for switching to development voltages. It is important, of course, that the voltage switching be accomplished without compromising control over the amplitude of the output voltages produced by the power supply.